opencl: add config option to allow use of CPU OpenCL devices

this is mainly for benchmarking purposes so users can try by themselves if they
doubt our statement that darktable's hand-optimized CPU code is faster than OpenCL-on-CPU :)
noise profile: canon 70d by john pham.
[l10n] Swedish update of a number of new preference entries
Update French translation.
Italian translation updated
Revert "Fix compile on systems not using X11"

This reverts commit 316b59c9de49965b32d16098a740355cb8d7f10e.

Preparations to revert 56d67620f985ab58f62b93967887147f8c400f66.
Revert "#9631: Hint GNOME 3 window manager to use dark window borders"

This reverts commit 56d67620f985ab58f62b93967887147f8c400f66.

This never worked, as reported by the reporter. Likely the realize function is
being assigned after the window is already realized.
Merge pull request #340 from bartokk/master

Italian translation updated